NED Abstract

Copyright by American Astronomical Society.
Reproduced by permission
1996ApJ...466..795H
THE ABSENCE OF X-RAY FLASHES FROM NEARBY GALAXIES AND THE GAMMA-RAY
BURST DISTANCE SCALE
T. T. HAMILTON
Department of Astronomy, California Institute of Technology,
Pasadena, CA 91125
E. V. GOTTHELF
Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight
Center, Greenbelt, MD 20771
AND
D. J. HELFAND
Department of Astronomy and Columbia Astrophysics Laboratory, Columbia
University, 538 West 120th Street, New York, NY 10027
Received 1995 March 17; accepted 1996 February 8
ABSTRACT
If typical gamma-ray bursts (GRBs) have X-ray counterparts similar to
those detected by Ginga, then sensitive-focusing X-ray telescopes will be
able to detect GRBs 3 orders of magnitude fainter than the detection
limit of the Burst and Transient Source Experiment (BATSE). If a
substantial portion of the burst population detected by BATSE originates
in a Galactic halo at distances greater than or equal to 150 kpc,
existing X-ray telescopes will be able to detect GRBs in external
galaxies out to a distance of at least 4.5 Mpc. As reported in Gotthelf,
Hamilton, & Helfand, the imaging proportional counter (IPC) on board the
Einstein Observatory detected 42 transient events with pointlike spatial
characteristics and timescales of less than 10 s. These events are
distributed isotropically on the sky; in particular, they are not
concentrated in the directions of nearby external galaxies. For halo
models of the BATSE bursts with radii of 150 kpc or greater, we would
expect to see several burst events in observations pointed toward nearby
galaxies. We see none. We therefore conclude that if the Ginga detections
are representative of the population of GRBs sampled by BATSE, GRBs
cannot originate in a Galactic halo population with limiting radii
between 150 and 400 kpc. Inasmuch as halos with limiting radii outside of
this range have been excluded by the BATSE isotropy measurements, our
result indicates that all halo models are excluded. This result is
independent of whether the flashes we do detect have an astronomical
origin.
Subject headings: gamma rays: bursts - surveys - X-rays: bursts